1. Field of the Invention
The present invention relates to a positive electrode active material for lithium ion battery, a positive electrode for lithium ion battery, and a lithium ion battery.
2. Description of Related Art
In general, as positive electrode active materials for lithium ion batteries, lithium-containing transition metal oxides are used. Specific examples thereof include lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), and lithium manganate (LiMn2O4). In order to improve characteristics (high capacity, cycling characteristics, storage characteristics, internal resistance reduction, and rate characteristics) and safety, combination of these oxides is progressed. Lithium ion batteries for large-size applications such as those for automobiles and road leveling are required to have different characteristics from prior art batteries for cellular telephones and personal computers. In particular, special emphasis is placed on good rate characteristics.
Improvement of rate characteristics has been attempted by various methods. For example, Patent document 1 discloses a layered lithium nickel complex oxide powder for lithium secondary battery positive electrode material composed of secondary particles prepared by aggregation of primary particles, the layered lithium nickel complex oxide powder for lithium secondary battery positive electrode material having a bulk density of 2.0 g/cc or more, an average primary particle size B of 0.1 to 1 μm, the secondary particles having a median diameter A of 9 to 20 μm, the ratio of the median diameter A of the secondary particles to the average primary particle size B, or A/B being from 10 to 200. The document describes that it provides a high density layered lithium nickel complex oxide powder for lithium secondary battery positive electrode material which allows the production of a lithium secondary battery having a high capacity and good rate characteristics.    (Patent document 1) Japanese Patent Application Publication No. 2007-214138